Keyboard with keys of transparent material



June 11, 1968 J. WIRTH 3,387,693

KEYBOARD WITH KEYS 0F TRANSPARENT MATERIAL Filed Dec. 20. 1966 INVENTOR. (JOHN/MES WIRTH United States Patent 3,387,693 KEYBOARD WITH KEYS 0F TRANSPARENT MATERIAL Johannes Wirth, Zurich, Switzerland, assignor to Wirth, Gallo & Co., Zurich, Switzerland Filed Dec. 20, 1966, Ser. No. 603,308

Claims priority, application Switzerland, Jan. 31, 1966,

1,407/ 66 7 Claims. (Cl. 197-98) ABSTRACT OF THE DISCLOSURE A key formed of transparent material and use together with a keyboard to form an optical system. The keys are disposed above a mounting plate in spaced relation therefrom at a distance substantially equal to the focal length of the optical system. In a normal condition, a reference character image seen through the key is indistinct but when the key is depressed the reference character image is clear and sharp.

The present invention relates to 'a keyboard with keys made of a transparent material, for instance in indicating, writing or calculating devices to be used in association with instruments, weighing machines or digital control means.

It is desirable in keyboards in which the operated keys are not pushed far below the general level of the other keys, that the depressed keys should be readily recognizable as having been operated and their value should be clearly readable. When the operated keys of a keyboard are not far below the general level of the rest of the keys it is sometimes difiicult to see which keys have been depressed when the keyboard is viewed from above, as is convenient. It has already been proposed to render the keyed value easily discernible by internally illuminating those keys that have been depressed. It is still a drawback of this arrangement that in bright light, particularly in direct sunlight, it is still difficult to identify the keys that have been depressed, unless a disproportionately large amuont of power is used for their illumination. If this were done the keyboard would also be unduly heated should the keys remain in an operated position for any length of time.

The proposed keyboard overcomes this drawback by disposing keys constituting optical systems in spaced relationship to a mounting plate above the plate at a distance which is at least substantially equal to the focal length of the optical sysem, in such manner that, when depressed, the keys move substantially into contact with the mounting plate.

An embodiment of the invention is schematically shown in the accompanying drawings in which:

FIG. 1 is an elevational section of part of a keyboard,

FIG. 2 is a side elevation of FIG. 1,

FIG. 3 is a plan view of FIG. 1,

FIG. 4 shows the path of the light rays when the key is not depressed,

FIG. 5 shows the path of the rays when the key is depressed,

FIG. 6 is a plan view of a key in the position according to FIG. 4,

FIG. 7 is a plan View of a key in the position according to FIG. 5, and

FIG. 8 is a vertical section of the head of a key.

FIG. 1 shows only the first four keys of a decade. Each key 8 is mounted on a rod 4 which is vertically slidably guided in two plates 5 and 9. Each key 8 is held in its upper position by a spring 7. When a key, such as 3,387,693 Patented June 11, 1968 key 3, is depressed it is retained in conventional manner in its depressed position until another key is depressed. When this is the case the first key 3 is released and its spring 7 returns it into its former position. A character, e.g., a numeral identifying the key is provided on plate 9 below each key. The keys 8 themselves constitute optical lens systems which have a focal length roughly equal to the distance between the plate 9 and the underside of the depressed key.

As shown in FIG. 3 the identifying numeral 0, l and 2 of the depressed keys are only indistinctly seen excessively magnified through the top of the keys, whereas the numeral identifying the key 3 that has been depressed appears sharp and normally magnified.

FIG. 4 illustrates the path of the rays when the key is not depressed. In this illustration it is assumed that the underside 10 of the key 8 is fiat. The numeral which is to be imaged is located on the plate 9 near the focus of the lens which forms the key. Consequently, the numeral 3, as shown in FIG. 6, will be greatly magnified and only part of it will be visible (rays m). For accentuating this effect the underside 10 of the key 8, as shown in FIG. 8 may be provided with a fine prismatic or pynamdial ribbing, for instance in the form of ribs spaced only 0.1 mm. apart. The same effect can be achieved by providing the underside 10 with a matt surface. The ribbed or matt surface results in the numeral being seen clearly and sharply defined only when the numeral is closed to or in contact with the underside of the key, whereas the image will be excessively magnified and blurred by the ribbing when the key is spaced away from plate 9 (rays S, image indistinct, as illustrated in FIG. 6).

FIGS. 5 and 7 show the path of the rays and the image when the key has been depressed.

FIG. 8 is a key composed of two elements of organic glass. An upper lens 11 may be concave-convex, whereas a lower lens 12 is plano-convex with the plane surface 10 facing downwards. This plane surface 10 may likewise be mad or ribbed.

The rod 4 carrying the key is only schematically shown. According to the application of the keyboard, means are connected to these rods for the generation of mechanical, electrical, optical or like signals. The nature of these means and of the signals that are transmitted may be of conventional kind.

I claim:

1. A keyboard comprising mounting plate means having on one face thereof a plurality of reference characters, a plurality of keys having a head portion formed from transparent material to constitute an optical lens system and a rod portion depending therefrom, said rod portion operatively mounting said keys on said mounting plate means, spring means normally biasing said keys to a spaced relationship with said mounting plate means at a distance at least substantially equal to the focal length of said optical system at which position said reference characters are normally over-magnified and therefore indistinct, said reference characters being normally magnified, readable and distinct when said keys are depressed substantially into contact with said mounting plate means.

2. A keyboard according to claim 1 in which said head portion is a solid element having a substantially convex upper surface and a substantially planar undersurface, the ratio of the radius of the upper surface to the thickness of said element being in the range of 1 to 1.7.

3. A keyboard according to claim 1 in which said head portion comprises a twin-lens optical system, the lower of said lenses having a substantially planar undersurface and :a convex upper surface, and the upper of said lenses being biconvex.

4. A keyboard according to claim 1 in which said head portion comprises a twin-lens optical system, the lower of said lenses having a substantially planar undersurface and a substantially convex upper surface, and the upper of said lenses being piano-convex.

5. A keyboard according to claim 1 in which said head portion comprises :a twin-lens optical system, the lower of said lenses having a substantially planar undersurface and a substantially convex upper surface, and the upper of said lenses being concave-convex.

6. A keyboard according to claim 1 in which the un- 1 derside of said lens system has a matt formed thereon to effect light dispersion.

7. A keyboard according to claim 1 in which the underside to said lens system has fine ribbing formed thereon to eifect light dispersion.

References Cited UNITED STATES PATENTS 430,774- 6/1890 Hamilton 197-102 867,868 10/1908 Beais 197-102 1,286,769 12/1918 Quentell 235-145 1,575,784 3/1926 OMeara 350-115 2,228,780 1/19 41 Roberts 197-98 2,234,954- 3/1941 Bergman 235-145 2,265,626 12/1941 Butler 235-145 3,237,591 3/1966 Pichel 235-145 2,642,226 5/1953 Luhn 35-145 OTHER REFERENCES IBM Technical Disclosure Bulletin, v01. 6, No. 1, June 1963, Article by E. V. Weber entitled Changeable Keyboard Labeling and Coding, p. 39.

IBM Tech. Disclosure Bulletin, vol. 3, No. 6, Novem- 15 ber 1960, Article by D. E. Eastwood entitled Key Top,

ROBERT E. PULFREY, Primary Examiner.

0 E. S. BURR, Examiner. 

